Objectives: To identify the most effective interventions for treating peri-implantitis around osseointegrated dental implants. Data sources: The Cochrane Oral Health Groups Trials Register, CENTRAL, MEDLINE and EMBASE were searched and several journals were handsearched with no language restriction up to January 2008. Review methods: Randomised controlled trials (RCTs) comparing interventions for treating peri-implantitis were eligible. Screening of studies, quality assessment and data extraction were conducted in duplicate. Missing information was requested. Outcome measures were: implant failure; complications; changes in radiographic marginal bone level, probing ‘attachment level (PAL), probing pocket depth (PPD), and recession; aesthetics evaluated by patients and dentists; cost and treatment time. Results: Ten eligible trials were identified, and seven were included (148 patients). They tested: (1) local antibiotics vs ultrasonic debridement; (2) adjunctive local antibiotics to debridement; (3) different techniques of subgingival debridement; (4) laser vs manual debridement and chlorhexidine irrigation/ gel; (5) systemic antibiotics plus resective surgery plus two local antibiotics with and without implant surface smoothening; and (6) nanocrystalline hydroxyapatite vs Bio-Oss and resorbable barriers. Follow up ranged from 3 months to 2 years. After 4 months, adjunctive local antibiotics to manual debridement in patients who lost at least 50% of peri-implant bone showed improved PAL and PPD (0.6 mm). After 6 months, peri-implant infrabony defects > 3 mm treated with Bio-Oss and barriers gained 0.5 mm more PAL and PPD than those treated with hydroxyapatite. In four trials subgingival mechanical debridement seemed to achieve results similar to more complex therapies. Conclusions: There is very little reliable evidence suggesting which could be the most effective interventions for peri-implantitis. Sample sizes were too small and follow up too short. This is not to say that currently used interventions are ineffective. Larger well-designed RCTs are needed.